With respect to a stay damper which assists in the opening of a swing-type vehicle rear door, JPH10-115340A and JPH11-201210A published in 1998 and 1999 by Japan Patent Office, respectively, propose a locking mechanism which automatically locks contraction of the stay damper from an elongated position.
The stay damper comprises a cylinder, a piston accommodated in the cylinder, and a piston rod connected to the piston and projecting from the cylinder in an axial direction. The base of the cylinder is connected to a vehicle body while the projecting end of the piston rod is connected to the door. The cylinder is charged with gas, and the piston rod is biased to project from the cylinder according to a gas pressure.
The piston rod is covered by a cylindrical cover. The cover is supported by the projecting end of the piston rod such that the cover can overlap the outer circumference of the cylinder and swing about the projecting end of the piston within a limited range.
A leaf spring is interposed between the piston rod and the cover. The leaf spring biases the cover to swing about the projecting end of the piston such that the tip of the cover displaces in a lateral direction.
When the door is closed, the stay damper is in a contracted state in which the piston rod is in the cylinder except for the projecting end thereof and the cover overlaps the outer circumference of the cylinder.
In contrast, when the piston rod is elongated to its maximum length as the door is opened, the cover does not overlap the cylinder any more and the tip of the cover is removed from the outer circumference of the cylinder. In this state, the leaf spring causes the cover to swing about the projecting end of the piston rod, and as a result, the cover is inclined with respect to the cylinder. Thus, the tip of the cover is offset from the cylinder tip in the lateral direction.
When the contracting force is applied to the piston rod, the tip of the cover abuts against the cylinder tip, thereby preventing the piston rod from contracting.
According to the above construction of the stay damper, when the door is fully open, the stay damper is automatically brought into a locked state in which contraction thereof is prevented and thereafter the door is supported in the fully open position by the stay damper.
When the door is to be closed, a lock release operation is required which is accomplished by shifting the tip of the cover from the lock position against the force of the spring in a lateral direction. After performing the lock release operation, the cover no longer interferes with the contracting piston rod and the stay damper contracts smoothly under an appropriate resistance due to the pressure of the gas in the cylinder.